Fluid Exchange & Edema PDF

Fluid Exchange & Edema PROF. TARIG H MERGHANI Learning Outcomes  Explain the mechanisms controlling fluid movement between the plasma and interstitial fluid,  Analyze factors that contribute to the development of edema, focusing on changes in Starling’s forces. Fluid exchang...

Fluid Exchange & Edema PROF. TARIG H MERGHANI Learning Outcomes  Explain the mechanisms controlling fluid movement between the plasma and interstitial fluid,  Analyze factors that contribute to the development of edema, focusing on changes in Starling’s forces. Fluid exchange Between Plasma & Interstitium  Occurs at the capillaries  Due to two types of pressure (Starling Forces):  Hydrostatic pressure (pressure of water on the vessel wall)  Oncotic pressure (osmotic pressure of protein) - Mainly albumin  Fluid exchange Between Plasma & Interstitium  The capillaries have two pressures: Capillary hydrostatic pressure (HPc, for filtration of fluid to outside)= 10-35mmHg Capillaryoncotic pressure (πC, for absorption of fluid)= 25 mmHg  Fluid exchange Between Plasma & Interstitium  The ISF has two pressures: ISF hydrostatic pressure (HPISF, against filtration from capillaries) oncotic pressure (πISF, against ISF absorption into capillaries)  Fluid exchange Between Plasma & Interstitium  Therefore, the forces that control fluid exchange between ISF and plasma in capillaries are four (known as Starling forces). Net Filtration Pressure (NFP)  NFP= HPc - HPISF - πc + πISF  Fluid exchange Between Plasma & Interstitium  ISF pressures are usually of low magnitude and antagonize each other; so, they are usually ignored. Net Filtration Pressure (NFP) o At the arteriolar end= (35-25) = +10 mmHg (i.e., net filtration) o At the veniolar end= (15-25) = -10 mmHg (i.e., net absorption) At the arterial end of capillaries:  The capillary hydrostatic pressure > oncotic pressure resulting in filtration of fluid At the venous end of capillaries:  The oncotic pressure < hydrostatic pressure resulting in absorption of 90% of filtered fluid At the venous end of capillaries:  The remaining 10% of filtered fluid is absorbed by the lymphatic vessels Edema  Defined as abnormal collection of fluid in the interstitium Mechanisms of edema 1- High HPc Caused by: Heart failure Venous obstruction (Deep vein thrombosis) Mechanisms of edema  2- Low OPc Caused by: Malnutrition Malabsorption Chronic liver disease Chronic renal disease (nephrotic syndrome) Mechanisms of edema 3- Lymphatic obstruction Caused by: Filariasis (elephantiasis) Tumors Surgical removal Mechanisms of edema  4- Increased permeability of capillaries to protein Caused by: Allergy Inflammation Burn Types of edema  Pitting and non pitting  Pitting edema  All causes of High HPc and low OPc Non-pitting edema  All causes of lymphatic obstruction and increased permeability of capillaries to protein  Types of edema  Generalized and localized Generalized edema  All causes of low capillary oncotic pressure  Congestive Heart failure  Localized edema  Lymphatic obstruction  Venous obstruction  Localized causes of increased permeability